// SPDX-License-Identifier: GPL-2.0-only
/*
 * RT-Mutexes: simple blocking mutual exclusion locks with PI support
 *
 * started by Ingo Molnar and Thomas Gleixner.
 *
 *  Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 *  Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
 *  Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
 *  Copyright (C) 2006 Esben Nielsen
 * Adaptive Spinlocks:
 *  Copyright (C) 2008 Novell, Inc., Gregory Haskins, Sven Dietrich,
 *				     and Peter Morreale,
 * Adaptive Spinlocks simplification:
 *  Copyright (C) 2008 Red Hat, Inc., Steven Rostedt <srostedt@redhat.com>
 *
 *  See Documentation/locking/rt-mutex-design.rst for details.
 */
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/sched/deadline.h>
#include <linux/sched/signal.h>
#include <linux/sched/rt.h>
#include <linux/sched/wake_q.h>
#include <linux/ww_mutex.h>

#include <trace/events/lock.h>

#define CONFIG_PREEMPT_RT 1

#include "rtmutex.h"

#ifndef WW_RT
#define build_ww_mutex() (false)
#define ww_container_of(rtm) NULL

static inline int __ww_mutex_add_waiter(struct rt_mutex_waiter *waiter,
                                        struct rt_mutex *lock,
                                        struct ww_acquire_ctx *ww_ctx,
                                        struct wake_q_head *wake_q)
{
    return 0;
}

static inline void __ww_mutex_check_waiters(struct rt_mutex *lock,
                                            struct ww_acquire_ctx *ww_ctx,
                                            struct wake_q_head *wake_q)
{
}

static inline void ww_mutex_lock_acquired(struct ww_mutex *lock,
                                          struct ww_acquire_ctx *ww_ctx)
{
}

static inline int __ww_mutex_check_kill(struct rt_mutex *lock,
                                        struct rt_mutex_waiter *waiter,
                                        struct ww_acquire_ctx *ww_ctx)
{
    return 0;
}

#else
#define build_ww_mutex() (true)
#define ww_container_of(rtm) container_of(rtm, struct ww_mutex, base)
#include "ww_mutex.h"
#endif

/*
 * lock->owner state tracking:
 *
 * lock->owner holds the task_struct pointer of the owner. Bit 0
 * is used to keep track of the "lock has waiters" state.
 *
 * owner	bit0
 * NULL		0	lock is free (fast acquire possible)
 * NULL		1	lock is free and has waiters and the top waiter
 *				is going to take the lock*
 * taskpointer	0	lock is held (fast release possible)
 * taskpointer	1	lock is held and has waiters**
 *
 * The fast atomic compare exchange based acquire and release is only
 * possible when bit 0 of lock->owner is 0.
 *
 * (*) It also can be a transitional state when grabbing the lock
 * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
 * we need to set the bit0 before looking at the lock, and the owner may be
 * NULL in this small time, hence this can be a transitional state.
 *
 * (**) There is a small time when bit 0 is set but there are no
 * waiters. This can happen when grabbing the lock in the slow path.
 * To prevent a cmpxchg of the owner releasing the lock, we need to
 * set this bit before looking at the lock.
 */

static __always_inline struct task_struct *
rt_mutex_owner_encode(struct rt_mutex_base *lock, struct task_struct *owner)
{
    unsigned long val = (unsigned long)owner;

    if (rt_mutex_has_waiters(lock))
        val |= RT_MUTEX_HAS_WAITERS;

    return (struct task_struct *)val;
}

static __always_inline void
rt_mutex_set_owner(struct rt_mutex_base *lock, struct task_struct *owner)
{
    /*
     * lock->wait_lock is held but explicit acquire semantics are needed
     * for a new lock owner so WRITE_ONCE is insufficient.
     */
    xchg_acquire(&lock->owner, rt_mutex_owner_encode(lock, owner));
}

static __always_inline void rt_mutex_clear_owner(struct rt_mutex_base *lock)
{
    /* lock->wait_lock is held so the unlock provides release semantics. */
    WRITE_ONCE(lock->owner, rt_mutex_owner_encode(lock, NULL));
}

static __always_inline void clear_rt_mutex_waiters(struct rt_mutex_base *lock)
{
    lock->owner = (struct task_struct *)((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
}

static __always_inline void
fixup_rt_mutex_waiters(struct rt_mutex_base *lock, bool acquire_lock)
{
    unsigned long owner, *p = (unsigned long *)&lock->owner;

    if (rt_mutex_has_waiters(lock))
        return;

    /*
     * The rbtree has no waiters enqueued, now make sure that the
     * lock->owner still has the waiters bit set, otherwise the
     * following can happen:
     *
     * CPU 0	CPU 1		CPU2
     * l->owner=T1
     *		rt_mutex_lock(l)
     *		lock(l->lock)
     *		l->owner = T1 | HAS_WAITERS;
     *		enqueue(T2)
     *		boost()
     *		  unlock(l->lock)
     *		block()
     *
     *				rt_mutex_lock(l)
     *				lock(l->lock)
     *				l->owner = T1 | HAS_WAITERS;
     *				enqueue(T3)
     *				boost()
     *				  unlock(l->lock)
     *				block()
     *		signal(->T2)	signal(->T3)
     *		lock(l->lock)
     *		dequeue(T2)
     *		deboost()
     *		  unlock(l->lock)
     *				lock(l->lock)
     *				dequeue(T3)
     *				 ==> wait list is empty
     *				deboost()
     *				 unlock(l->lock)
     *		lock(l->lock)
     *		fixup_rt_mutex_waiters()
     *		  if (wait_list_empty(l) {
     *		    l->owner = owner
     *		    owner = l->owner & ~HAS_WAITERS;
     *		      ==> l->owner = T1
     *		  }
     *				lock(l->lock)
     * rt_mutex_unlock(l)		fixup_rt_mutex_waiters()
     *				  if (wait_list_empty(l) {
     *				    owner = l->owner & ~HAS_WAITERS;
     * cmpxchg(l->owner, T1, NULL)
     *  ===> Success (l->owner = NULL)
     *
     *				    l->owner = owner
     *				      ==> l->owner = T1
     *				  }
     *
     * With the check for the waiter bit in place T3 on CPU2 will not
     * overwrite. All tasks fiddling with the waiters bit are
     * serialized by l->lock, so nothing else can modify the waiters
     * bit. If the bit is set then nothing can change l->owner either
     * so the simple RMW is safe. The cmpxchg() will simply fail if it
     * happens in the middle of the RMW because the waiters bit is
     * still set.
     */
    owner = READ_ONCE(*p);
    if (owner & RT_MUTEX_HAS_WAITERS)
    {
        /*
         * See rt_mutex_set_owner() and rt_mutex_clear_owner() on
         * why xchg_acquire() is used for updating owner for
         * locking and WRITE_ONCE() for unlocking.
         *
         * WRITE_ONCE() would work for the acquire case too, but
         * in case that the lock acquisition failed it might
         * force other lockers into the slow path unnecessarily.
         */
        if (acquire_lock)
            xchg_acquire(p, owner & ~RT_MUTEX_HAS_WAITERS);
        else
            WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
    }
}

/*
 * We can speed up the acquire/release, if there's no debugging state to be
 * set up.
 */
#ifndef CONFIG_DEBUG_RT_MUTEXES
static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
                                                     struct task_struct *old,
                                                     struct task_struct *new)
{
    return try_cmpxchg_acquire(&lock->owner, &old, new);
}

static __always_inline bool rt_mutex_try_acquire(struct rt_mutex_base *lock)
{
    return rt_mutex_cmpxchg_acquire(lock, NULL, current);
}

static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
                                                     struct task_struct *old,
                                                     struct task_struct *new)
{
    return try_cmpxchg_release(&lock->owner, &old, new);
}

/*
 * Callers must hold the ->wait_lock -- which is the whole purpose as we force
 * all future threads that attempt to [Rmw] the lock to the slowpath. As such
 * relaxed semantics suffice.
 */
static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
{
    unsigned long *p = (unsigned long *)&lock->owner;
    unsigned long owner, new;

    owner = READ_ONCE(*p);
    do
    {
        new = owner | RT_MUTEX_HAS_WAITERS;
    } while (!try_cmpxchg_relaxed(p, &owner, new));

    /*
     * The cmpxchg loop above is relaxed to avoid back-to-back ACQUIRE
     * operations in the event of contention. Ensure the successful
     * cmpxchg is visible.
     */
    smp_mb__after_atomic();
}

/*
 * Safe fastpath aware unlock:
 * 1) Clear the waiters bit
 * 2) Drop lock->wait_lock
 * 3) Try to unlock the lock with cmpxchg
 */
static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock,
                                                 unsigned long flags)
    __releases(lock->wait_lock)
{
    struct task_struct *owner = rt_mutex_owner(lock);

    clear_rt_mutex_waiters(lock);
    raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
    /*
     * If a new waiter comes in between the unlock and the cmpxchg
     * we have two situations:
     *
     * unlock(wait_lock);
     *					lock(wait_lock);
     * cmpxchg(p, owner, 0) == owner
     *					mark_rt_mutex_waiters(lock);
     *					acquire(lock);
     * or:
     *
     * unlock(wait_lock);
     *					lock(wait_lock);
     *					mark_rt_mutex_waiters(lock);
     *
     * cmpxchg(p, owner, 0) != owner
     *					enqueue_waiter();
     *					unlock(wait_lock);
     * lock(wait_lock);
     * wake waiter();
     * unlock(wait_lock);
     *					lock(wait_lock);
     *					acquire(lock);
     */
    return rt_mutex_cmpxchg_release(lock, owner, NULL);
}

#else
static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
                                                     struct task_struct *old,
                                                     struct task_struct *new)
{
    return false;
}

static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock);

static __always_inline bool rt_mutex_try_acquire(struct rt_mutex_base *lock)
{
    /*
     * With debug enabled rt_mutex_cmpxchg trylock() will always fail.
     *
     * Avoid unconditionally taking the slow path by using
     * rt_mutex_slow_trylock() which is covered by the debug code and can
     * acquire a non-contended rtmutex.
     */
    return rt_mutex_slowtrylock(lock);
}

static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
                                                     struct task_struct *old,
                                                     struct task_struct *new)
{
    return false;
}

static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
{
    lock->owner = (struct task_struct *)((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
}

/*
 * Simple slow path only version: lock->owner is protected by lock->wait_lock.
 */
static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock,
                                                 unsigned long flags)
    __releases(lock->wait_lock)
{
    lock->owner = NULL;
    raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
    return true;
}
#endif

static __always_inline int __waiter_prio(struct task_struct *task)
{
    int prio = task->prio;

    if (!rt_or_dl_prio(prio))
        return DEFAULT_PRIO;

    return prio;
}

/*
 * Update the waiter->tree copy of the sort keys.
 */
static __always_inline void
waiter_update_prio(struct rt_mutex_waiter *waiter, struct task_struct *task)
{
    lockdep_assert_held(&waiter->lock->wait_lock);
    lockdep_assert(RB_EMPTY_NODE(&waiter->tree.entry));

    waiter->tree.prio = __waiter_prio(task);
    waiter->tree.deadline = task->dl.deadline;
}

/*
 * Update the waiter->pi_tree copy of the sort keys (from the tree copy).
 */
static __always_inline void
waiter_clone_prio(struct rt_mutex_waiter *waiter, struct task_struct *task)
{
    lockdep_assert_held(&waiter->lock->wait_lock);
    lockdep_assert_held(&task->pi_lock);
    lockdep_assert(RB_EMPTY_NODE(&waiter->pi_tree.entry));

    waiter->pi_tree.prio = waiter->tree.prio;
    waiter->pi_tree.deadline = waiter->tree.deadline;
}

/*
 * Only use with rt_waiter_node_{less,equal}()
 */
#define task_to_waiter_node(p) \
    &(struct rt_waiter_node) { .prio = __waiter_prio(p), .deadline = (p)->dl.deadline }
#define task_to_waiter(p) \
    &(struct rt_mutex_waiter) { .tree = *task_to_waiter_node(p) }

static __always_inline int rt_waiter_node_less(struct rt_waiter_node *left,
                                               struct rt_waiter_node *right)
{
    if (left->prio < right->prio)
        return 1;

    /*
     * If both waiters have dl_prio(), we check the deadlines of the
     * associated tasks.
     * If left waiter has a dl_prio(), and we didn't return 1 above,
     * then right waiter has a dl_prio() too.
     */
    if (dl_prio(left->prio))
        return dl_time_before(left->deadline, right->deadline);

    return 0;
}

static __always_inline int rt_waiter_node_equal(struct rt_waiter_node *left,
                                                struct rt_waiter_node *right)
{
    if (left->prio != right->prio)
        return 0;

    /*
     * If both waiters have dl_prio(), we check the deadlines of the
     * associated tasks.
     * If left waiter has a dl_prio(), and we didn't return 0 above,
     * then right waiter has a dl_prio() too.
     */
    if (dl_prio(left->prio))
        return left->deadline == right->deadline;

    return 1;
}

static inline bool rt_mutex_steal(struct rt_mutex_waiter *waiter,
                                  struct rt_mutex_waiter *top_waiter)
{
    if (rt_waiter_node_less(&waiter->tree, &top_waiter->tree))
        return true;

#ifdef RT_MUTEX_BUILD_SPINLOCKS
    /*
     * Note that RT tasks are excluded from same priority (lateral)
     * steals to prevent the introduction of an unbounded latency.
     */
    if (rt_or_dl_prio(waiter->tree.prio))
        return false;

    return rt_waiter_node_equal(&waiter->tree, &top_waiter->tree);
#else
    return false;
#endif
}

#define __node_2_waiter(node) \
    rb_entry((node), struct rt_mutex_waiter, tree.entry)

static __always_inline bool __waiter_less(struct rb_node *a, const struct rb_node *b)
{
    struct rt_mutex_waiter *aw = __node_2_waiter(a);
    struct rt_mutex_waiter *bw = __node_2_waiter(b);

    if (rt_waiter_node_less(&aw->tree, &bw->tree))
        return 1;

    if (!build_ww_mutex())
        return 0;

    if (rt_waiter_node_less(&bw->tree, &aw->tree))
        return 0;

    /* NOTE: relies on waiter->ww_ctx being set before insertion */
    if (aw->ww_ctx)
    {
        if (!bw->ww_ctx)
            return 1;

        return (signed long)(aw->ww_ctx->stamp -
                             bw->ww_ctx->stamp) < 0;
    }

    return 0;
}

static __always_inline void
rt_mutex_enqueue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter)
{
    lockdep_assert_held(&lock->wait_lock);

    rb_add_cached(&waiter->tree.entry, &lock->waiters, __waiter_less);
}

static __always_inline void
rt_mutex_dequeue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter)
{
    lockdep_assert_held(&lock->wait_lock);

    if (RB_EMPTY_NODE(&waiter->tree.entry))
        return;

    rb_erase_cached(&waiter->tree.entry, &lock->waiters);
    RB_CLEAR_NODE(&waiter->tree.entry);
}

#define __node_2_rt_node(node) \
    rb_entry((node), struct rt_waiter_node, entry)

static __always_inline bool __pi_waiter_less(struct rb_node *a, const struct rb_node *b)
{
    return rt_waiter_node_less(__node_2_rt_node(a), __node_2_rt_node(b));
}

static __always_inline void
rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
{
    lockdep_assert_held(&task->pi_lock);

    rb_add_cached(&waiter->pi_tree.entry, &task->pi_waiters, __pi_waiter_less);
}

static __always_inline void
rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
{
    lockdep_assert_held(&task->pi_lock);

    if (RB_EMPTY_NODE(&waiter->pi_tree.entry))
        return;

    rb_erase_cached(&waiter->pi_tree.entry, &task->pi_waiters);
    RB_CLEAR_NODE(&waiter->pi_tree.entry);
}

static __always_inline void rt_mutex_adjust_prio(struct rt_mutex_base *lock,
                                                 struct task_struct *p)
{
    struct task_struct *pi_task = NULL;

    lockdep_assert_held(&lock->wait_lock);
    lockdep_assert(rt_mutex_owner(lock) == p);
    lockdep_assert_held(&p->pi_lock);

    if (task_has_pi_waiters(p))
        pi_task = task_top_pi_waiter(p)->task;

    rt_mutex_setprio(p, pi_task);
}

/* RT mutex specific wake_q wrappers */
static __always_inline void rt_mutex_wake_q_add_task(struct rt_wake_q_head *wqh,
                                                     struct task_struct *task,
                                                     unsigned int wake_state)
{
    if (IS_ENABLED(CONFIG_PREEMPT_RT) && wake_state == TASK_RTLOCK_WAIT)
    {
        if (IS_ENABLED(CONFIG_PROVE_LOCKING))
            WARN_ON_ONCE(wqh->rtlock_task);
        get_task_struct(task);
        wqh->rtlock_task = task;
    }
    else
    {
        wake_q_add(&wqh->head, task);
    }
}

static __always_inline void rt_mutex_wake_q_add(struct rt_wake_q_head *wqh,
                                                struct rt_mutex_waiter *w)
{
    rt_mutex_wake_q_add_task(wqh, w->task, w->wake_state);
}

static __always_inline void rt_mutex_wake_up_q(struct rt_wake_q_head *wqh)
{
    if (IS_ENABLED(CONFIG_PREEMPT_RT) && wqh->rtlock_task)
    {
        wake_up_state(wqh->rtlock_task, TASK_RTLOCK_WAIT);
        put_task_struct(wqh->rtlock_task);
        wqh->rtlock_task = NULL;
    }

    if (!wake_q_empty(&wqh->head))
        wake_up_q(&wqh->head);

    /* Pairs with preempt_disable() in mark_wakeup_next_waiter() */
    preempt_enable();
}

/*
 * Deadlock detection is conditional:
 *
 * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
 * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
 *
 * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
 * conducted independent of the detect argument.
 *
 * If the waiter argument is NULL this indicates the deboost path and
 * deadlock detection is disabled independent of the detect argument
 * and the config settings.
 */
static __always_inline bool
rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
                              enum rtmutex_chainwalk chwalk)
{
    if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
        return waiter != NULL;
    return chwalk == RT_MUTEX_FULL_CHAINWALK;
}

static __always_inline struct rt_mutex_base *task_blocked_on_lock(struct task_struct *p)
{
    return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
}

/*
 * Adjust the priority chain. Also used for deadlock detection.
 * Decreases task's usage by one - may thus free the task.
 *
 * @task:	the task owning the mutex (owner) for which a chain walk is
 *		probably needed
 * @chwalk:	do we have to carry out deadlock detection?
 * @orig_lock:	the mutex (can be NULL if we are walking the chain to recheck
 *		things for a task that has just got its priority adjusted, and
 *		is waiting on a mutex)
 * @next_lock:	the mutex on which the owner of @orig_lock was blocked before
 *		we dropped its pi_lock. Is never dereferenced, only used for
 *		comparison to detect lock chain changes.
 * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
 *		its priority to the mutex owner (can be NULL in the case
 *		depicted above or if the top waiter is gone away and we are
 *		actually deboosting the owner)
 * @top_task:	the current top waiter
 *
 * Returns 0 or -EDEADLK.
 *
 * Chain walk basics and protection scope
 *
 * [R] refcount on task
 * [Pn] task->pi_lock held
 * [L] rtmutex->wait_lock held
 *
 * Normal locking order:
 *
 *   rtmutex->wait_lock
 *     task->pi_lock
 *
 * Step	Description				Protected by
 *	function arguments:
 *	@task					[R]
 *	@orig_lock if != NULL			@top_task is blocked on it
 *	@next_lock				Unprotected. Cannot be
 *						dereferenced. Only used for
 *						comparison.
 *	@orig_waiter if != NULL			@top_task is blocked on it
 *	@top_task				current, or in case of proxy
 *						locking protected by calling
 *						code
 *	again:
 *	  loop_sanity_check();
 *	retry:
 * [1]	  lock(task->pi_lock);			[R] acquire [P1]
 * [2]	  waiter = task->pi_blocked_on;		[P1]
 * [3]	  check_exit_conditions_1();		[P1]
 * [4]	  lock = waiter->lock;			[P1]
 * [5]	  if (!try_lock(lock->wait_lock)) {	[P1] try to acquire [L]
 *	    unlock(task->pi_lock);		release [P1]
 *	    goto retry;
 *	  }
 * [6]	  check_exit_conditions_2();		[P1] + [L]
 * [7]	  requeue_lock_waiter(lock, waiter);	[P1] + [L]
 * [8]	  unlock(task->pi_lock);		release [P1]
 *	  put_task_struct(task);		release [R]
 * [9]	  check_exit_conditions_3();		[L]
 * [10]	  task = owner(lock);			[L]
 *	  get_task_struct(task);		[L] acquire [R]
 *	  lock(task->pi_lock);			[L] acquire [P2]
 * [11]	  requeue_pi_waiter(tsk, waiters(lock));[P2] + [L]
 * [12]	  check_exit_conditions_4();		[P2] + [L]
 * [13]	  unlock(task->pi_lock);		release [P2]
 *	  unlock(lock->wait_lock);		release [L]
 *	  goto again;
 *
 * Where P1 is the blocking task and P2 is the lock owner; going up one step
 * the owner becomes the next blocked task etc..
 *
 *
 */
static int __sched rt_mutex_adjust_prio_chain(struct task_struct *task,
                                              enum rtmutex_chainwalk chwalk,
                                              struct rt_mutex_base *orig_lock,
                                              struct rt_mutex_base *next_lock,
                                              struct rt_mutex_waiter *orig_waiter,
                                              struct task_struct *top_task)
{
    struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
    struct rt_mutex_waiter *prerequeue_top_waiter;
    int ret = 0, depth = 0;
    struct rt_mutex_base *lock;
    bool detect_deadlock;
    bool requeue = true;

    detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);

    /*
     * The (de)boosting is a step by step approach with a lot of
     * pitfalls. We want this to be preemptible and we want hold a
     * maximum of two locks per step. So we have to check
     * carefully whether things change under us.
     */
again:
    /*
     * We limit the lock chain length for each invocation.
     */
    if (++depth > max_lock_depth)
    {
        static int prev_max;

        /*
         * Print this only once. If the admin changes the limit,
         * print a new message when reaching the limit again.
         */
        if (prev_max != max_lock_depth)
        {
            prev_max = max_lock_depth;
        }
        put_task_struct(task);

        return -EDEADLK;
    }

    /*
     * We are fully preemptible here and only hold the refcount on
     * @task. So everything can have changed under us since the
     * caller or our own code below (goto retry/again) dropped all
     * locks.
     */
retry:
    /*
     * [1] Task cannot go away as we did a get_task() before !
     */
    raw_spin_lock_irq(&task->pi_lock);

    /*
     * [2] Get the waiter on which @task is blocked on.
     */
    waiter = task->pi_blocked_on;

    /*
     * [3] check_exit_conditions_1() protected by task->pi_lock.
     */

    /*
     * Check whether the end of the boosting chain has been
     * reached or the state of the chain has changed while we
     * dropped the locks.
     */
    if (!waiter)
        goto out_unlock_pi;

    /*
     * Check the orig_waiter state. After we dropped the locks,
     * the previous owner of the lock might have released the lock.
     */
    if (orig_waiter && !rt_mutex_owner(orig_lock))
        goto out_unlock_pi;

    /*
     * We dropped all locks after taking a refcount on @task, so
     * the task might have moved on in the lock chain or even left
     * the chain completely and blocks now on an unrelated lock or
     * on @orig_lock.
     *
     * We stored the lock on which @task was blocked in @next_lock,
     * so we can detect the chain change.
     */
    if (next_lock != waiter->lock)
        goto out_unlock_pi;

    /*
     * There could be 'spurious' loops in the lock graph due to ww_mutex,
     * consider:
     *
     *   P1: A, ww_A, ww_B
     *   P2: ww_B, ww_A
     *   P3: A
     *
     * P3 should not return -EDEADLK because it gets trapped in the cycle
     * created by P1 and P2 (which will resolve -- and runs into
     * max_lock_depth above). Therefore disable detect_deadlock such that
     * the below termination condition can trigger once all relevant tasks
     * are boosted.
     *
     * Even when we start with ww_mutex we can disable deadlock detection,
     * since we would supress a ww_mutex induced deadlock at [6] anyway.
     * Supressing it here however is not sufficient since we might still
     * hit [6] due to adjustment driven iteration.
     *
     * NOTE: if someone were to create a deadlock between 2 ww_classes we'd
     * utterly fail to report it; lockdep should.
     */
    if (IS_ENABLED(CONFIG_PREEMPT_RT) && waiter->ww_ctx && detect_deadlock)
        detect_deadlock = false;

    /*
     * Drop out, when the task has no waiters. Note,
     * top_waiter can be NULL, when we are in the deboosting
     * mode!
     */
    if (top_waiter)
    {
        if (!task_has_pi_waiters(task))
            goto out_unlock_pi;
        /*
         * If deadlock detection is off, we stop here if we
         * are not the top pi waiter of the task. If deadlock
         * detection is enabled we continue, but stop the
         * requeueing in the chain walk.
         */
        if (top_waiter != task_top_pi_waiter(task))
        {
            if (!detect_deadlock)
                goto out_unlock_pi;
            else
                requeue = false;
        }
    }

    /*
     * If the waiter priority is the same as the task priority
     * then there is no further priority adjustment necessary.  If
     * deadlock detection is off, we stop the chain walk. If its
     * enabled we continue, but stop the requeueing in the chain
     * walk.
     */
    if (rt_waiter_node_equal(&waiter->tree, task_to_waiter_node(task)))
    {
        if (!detect_deadlock)
            goto out_unlock_pi;
        else
            requeue = false;
    }

    /*
     * [4] Get the next lock; per holding task->pi_lock we can't unblock
     * and guarantee @lock's existence.
     */
    lock = waiter->lock;
    /*
     * [5] We need to trylock here as we are holding task->pi_lock,
     * which is the reverse lock order versus the other rtmutex
     * operations.
     *
     * Per the above, holding task->pi_lock guarantees lock exists, so
     * inverting this lock order is infeasible from a life-time
     * perspective.
     */
    if (!raw_spin_trylock(&lock->wait_lock))
    {
        raw_spin_unlock_irq(&task->pi_lock);
        cpu_relax();
        goto retry;
    }

    /*
     * [6] check_exit_conditions_2() protected by task->pi_lock and
     * lock->wait_lock.
     *
     * Deadlock detection. If the lock is the same as the original
     * lock which caused us to walk the lock chain or if the
     * current lock is owned by the task which initiated the chain
     * walk, we detected a deadlock.
     */
    if (lock == orig_lock || rt_mutex_owner(lock) == top_task)
    {
        ret = -EDEADLK;

        /*
         * When the deadlock is due to ww_mutex; also see above. Don't
         * report the deadlock and instead let the ww_mutex wound/die
         * logic pick which of the contending threads gets -EDEADLK.
         *
         * NOTE: assumes the cycle only contains a single ww_class; any
         * other configuration and we fail to report; also, see
         * lockdep.
         */
        if (IS_ENABLED(CONFIG_PREEMPT_RT) && orig_waiter && orig_waiter->ww_ctx)
            ret = 0;

        raw_spin_unlock(&lock->wait_lock);
        goto out_unlock_pi;
    }

    /*
     * If we just follow the lock chain for deadlock detection, no
     * need to do all the requeue operations. To avoid a truckload
     * of conditionals around the various places below, just do the
     * minimum chain walk checks.
     */
    if (!requeue)
    {
        /*
         * No requeue[7] here. Just release @task [8]
         */
        raw_spin_unlock(&task->pi_lock);
        put_task_struct(task);

        /*
         * [9] check_exit_conditions_3 protected by lock->wait_lock.
         * If there is no owner of the lock, end of chain.
         */
        if (!rt_mutex_owner(lock))
        {
            raw_spin_unlock_irq(&lock->wait_lock);
            return 0;
        }

        /* [10] Grab the next task, i.e. owner of @lock */
        task = get_task_struct(rt_mutex_owner(lock));
        raw_spin_lock(&task->pi_lock);

        /*
         * No requeue [11] here. We just do deadlock detection.
         *
         * [12] Store whether owner is blocked
         * itself. Decision is made after dropping the locks
         */
        next_lock = task_blocked_on_lock(task);
        /*
         * Get the top waiter for the next iteration
         */
        top_waiter = rt_mutex_top_waiter(lock);

        /* [13] Drop locks */
        raw_spin_unlock(&task->pi_lock);
        raw_spin_unlock_irq(&lock->wait_lock);

        /* If owner is not blocked, end of chain. */
        if (!next_lock)
            goto out_put_task;
        goto again;
    }

    /*
     * Store the current top waiter before doing the requeue
     * operation on @lock. We need it for the boost/deboost
     * decision below.
     */
    prerequeue_top_waiter = rt_mutex_top_waiter(lock);

    /* [7] Requeue the waiter in the lock waiter tree. */
    rt_mutex_dequeue(lock, waiter);

    /*
     * Update the waiter prio fields now that we're dequeued.
     *
     * These values can have changed through either:
     *
     *   sys_sched_set_scheduler() / sys_sched_setattr()
     *
     * or
     *
     *   DL CBS enforcement advancing the effective deadline.
     */
    waiter_update_prio(waiter, task);

    rt_mutex_enqueue(lock, waiter);

    /*
     * [8] Release the (blocking) task in preparation for
     * taking the owner task in [10].
     *
     * Since we hold lock->waiter_lock, task cannot unblock, even if we
     * release task->pi_lock.
     */
    raw_spin_unlock(&task->pi_lock);
    put_task_struct(task);

    /*
     * [9] check_exit_conditions_3 protected by lock->wait_lock.
     *
     * We must abort the chain walk if there is no lock owner even
     * in the dead lock detection case, as we have nothing to
     * follow here. This is the end of the chain we are walking.
     */
    if (!rt_mutex_owner(lock))
    {
        /*
         * If the requeue [7] above changed the top waiter,
         * then we need to wake the new top waiter up to try
         * to get the lock.
         */
        top_waiter = rt_mutex_top_waiter(lock);
        if (prerequeue_top_waiter != top_waiter)
            wake_up_state(top_waiter->task, top_waiter->wake_state);
        raw_spin_unlock_irq(&lock->wait_lock);
        return 0;
    }

    /*
     * [10] Grab the next task, i.e. the owner of @lock
     *
     * Per holding lock->wait_lock and checking for !owner above, there
     * must be an owner and it cannot go away.
     */
    task = get_task_struct(rt_mutex_owner(lock));
    raw_spin_lock(&task->pi_lock);

    /* [11] requeue the pi waiters if necessary */
    if (waiter == rt_mutex_top_waiter(lock))
    {
        /*
         * The waiter became the new top (highest priority)
         * waiter on the lock. Replace the previous top waiter
         * in the owner tasks pi waiters tree with this waiter
         * and adjust the priority of the owner.
         */
        rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
        waiter_clone_prio(waiter, task);
        rt_mutex_enqueue_pi(task, waiter);
        rt_mutex_adjust_prio(lock, task);
    }
    else if (prerequeue_top_waiter == waiter)
    {
        /*
         * The waiter was the top waiter on the lock, but is
         * no longer the top priority waiter. Replace waiter in
         * the owner tasks pi waiters tree with the new top
         * (highest priority) waiter and adjust the priority
         * of the owner.
         * The new top waiter is stored in @waiter so that
         * @waiter == @top_waiter evaluates to true below and
         * we continue to deboost the rest of the chain.
         */
        rt_mutex_dequeue_pi(task, waiter);
        waiter = rt_mutex_top_waiter(lock);
        waiter_clone_prio(waiter, task);
        rt_mutex_enqueue_pi(task, waiter);
        rt_mutex_adjust_prio(lock, task);
    }
    else
    {
        /*
         * Nothing changed. No need to do any priority
         * adjustment.
         */
    }

    /*
     * [12] check_exit_conditions_4() protected by task->pi_lock
     * and lock->wait_lock. The actual decisions are made after we
     * dropped the locks.
     *
     * Check whether the task which owns the current lock is pi
     * blocked itself. If yes we store a pointer to the lock for
     * the lock chain change detection above. After we dropped
     * task->pi_lock next_lock cannot be dereferenced anymore.
     */
    next_lock = task_blocked_on_lock(task);
    /*
     * Store the top waiter of @lock for the end of chain walk
     * decision below.
     */
    top_waiter = rt_mutex_top_waiter(lock);

    /* [13] Drop the locks */
    raw_spin_unlock(&task->pi_lock);
    raw_spin_unlock_irq(&lock->wait_lock);

    /*
     * Make the actual exit decisions [12], based on the stored
     * values.
     *
     * We reached the end of the lock chain. Stop right here. No
     * point to go back just to figure that out.
     */
    if (!next_lock)
        goto out_put_task;

    /*
     * If the current waiter is not the top waiter on the lock,
     * then we can stop the chain walk here if we are not in full
     * deadlock detection mode.
     */
    if (!detect_deadlock && waiter != top_waiter)
        goto out_put_task;

    goto again;

out_unlock_pi:
    raw_spin_unlock_irq(&task->pi_lock);
out_put_task:
    put_task_struct(task);

    return ret;
}

/*
 * Try to take an rt-mutex
 *
 * Must be called with lock->wait_lock held and interrupts disabled
 *
 * @lock:   The lock to be acquired.
 * @task:   The task which wants to acquire the lock
 * @waiter: The waiter that is queued to the lock's wait tree if the
 *	    callsite called task_blocked_on_lock(), otherwise NULL
 */
static int __sched
try_to_take_rt_mutex(struct rt_mutex_base *lock, struct task_struct *task,
                     struct rt_mutex_waiter *waiter)
{
    lockdep_assert_held(&lock->wait_lock);

    /*
     * Before testing whether we can acquire @lock, we set the
     * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
     * other tasks which try to modify @lock into the slow path
     * and they serialize on @lock->wait_lock.
     *
     * The RT_MUTEX_HAS_WAITERS bit can have a transitional state
     * as explained at the top of this file if and only if:
     *
     * - There is a lock owner. The caller must fixup the
     *   transient state if it does a trylock or leaves the lock
     *   function due to a signal or timeout.
     *
     * - @task acquires the lock and there are no other
     *   waiters. This is undone in rt_mutex_set_owner(@task) at
     *   the end of this function.
     */
    mark_rt_mutex_waiters(lock);

    /*
     * If @lock has an owner, give up.
     */
    if (rt_mutex_owner(lock))
        return 0;

    /*
     * If @waiter != NULL, @task has already enqueued the waiter
     * into @lock waiter tree. If @waiter == NULL then this is a
     * trylock attempt.
     */
    if (waiter)
    {
        struct rt_mutex_waiter *top_waiter = rt_mutex_top_waiter(lock);

        /*
         * If waiter is the highest priority waiter of @lock,
         * or allowed to steal it, take it over.
         */
        if (waiter == top_waiter || rt_mutex_steal(waiter, top_waiter))
        {
            /*
             * We can acquire the lock. Remove the waiter from the
             * lock waiters tree.
             */
            rt_mutex_dequeue(lock, waiter);
        }
        else
        {
            return 0;
        }
    }
    else
    {
        /*
         * If the lock has waiters already we check whether @task is
         * eligible to take over the lock.
         *
         * If there are no other waiters, @task can acquire
         * the lock.  @task->pi_blocked_on is NULL, so it does
         * not need to be dequeued.
         */
        if (rt_mutex_has_waiters(lock))
        {
            /* Check whether the trylock can steal it. */
            if (!rt_mutex_steal(task_to_waiter(task),
                                rt_mutex_top_waiter(lock)))
                return 0;

            /*
             * The current top waiter stays enqueued. We
             * don't have to change anything in the lock
             * waiters order.
             */
        }
        else
        {
            /*
             * No waiters. Take the lock without the
             * pi_lock dance.@task->pi_blocked_on is NULL
             * and we have no waiters to enqueue in @task
             * pi waiters tree.
             */
            goto takeit;
        }
    }

    /*
     * Clear @task->pi_blocked_on. Requires protection by
     * @task->pi_lock. Redundant operation for the @waiter == NULL
     * case, but conditionals are more expensive than a redundant
     * store.
     */
    raw_spin_lock(&task->pi_lock);
    task->pi_blocked_on = NULL;
    /*
     * Finish the lock acquisition. @task is the new owner. If
     * other waiters exist we have to insert the highest priority
     * waiter into @task->pi_waiters tree.
     */
    if (rt_mutex_has_waiters(lock))
        rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
    raw_spin_unlock(&task->pi_lock);

takeit:
    /*
     * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
     * are still waiters or clears it.
     */
    rt_mutex_set_owner(lock, task);

    return 1;
}

/*
 * Task blocks on lock.
 *
 * Prepare waiter and propagate pi chain
 *
 * This must be called with lock->wait_lock held and interrupts disabled
 */
static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,
                                           struct rt_mutex_waiter *waiter,
                                           struct task_struct *task,
                                           struct ww_acquire_ctx *ww_ctx,
                                           enum rtmutex_chainwalk chwalk,
                                           struct wake_q_head *wake_q)
{
    struct task_struct *owner = rt_mutex_owner(lock);
    struct rt_mutex_waiter *top_waiter = waiter;
    struct rt_mutex_base *next_lock;
    int chain_walk = 0, res;

    lockdep_assert_held(&lock->wait_lock);

    /*
     * Early deadlock detection. We really don't want the task to
     * enqueue on itself just to untangle the mess later. It's not
     * only an optimization. We drop the locks, so another waiter
     * can come in before the chain walk detects the deadlock. So
     * the other will detect the deadlock and return -EDEADLOCK,
     * which is wrong, as the other waiter is not in a deadlock
     * situation.
     *
     * Except for ww_mutex, in that case the chain walk must already deal
     * with spurious cycles, see the comments at [3] and [6].
     */
    if (owner == task && !(build_ww_mutex() && ww_ctx))
        return -EDEADLK;

    raw_spin_lock(&task->pi_lock);
    waiter->task = task;
    waiter->lock = lock;
    waiter_update_prio(waiter, task);
    waiter_clone_prio(waiter, task);

    /* Get the top priority waiter on the lock */
    if (rt_mutex_has_waiters(lock))
        top_waiter = rt_mutex_top_waiter(lock);
    rt_mutex_enqueue(lock, waiter);

    task->pi_blocked_on = waiter;

    raw_spin_unlock(&task->pi_lock);

    if (build_ww_mutex() && ww_ctx)
    {
        struct rt_mutex *rtm;

        /* Check whether the waiter should back out immediately */
        rtm = container_of(lock, struct rt_mutex, rtmutex);
        res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx, wake_q);
        if (res)
        {
            raw_spin_lock(&task->pi_lock);
            rt_mutex_dequeue(lock, waiter);
            task->pi_blocked_on = NULL;
            raw_spin_unlock(&task->pi_lock);
            return res;
        }
    }

    if (!owner)
        return 0;

    raw_spin_lock(&owner->pi_lock);
    if (waiter == rt_mutex_top_waiter(lock))
    {
        rt_mutex_dequeue_pi(owner, top_waiter);
        rt_mutex_enqueue_pi(owner, waiter);

        rt_mutex_adjust_prio(lock, owner);
        if (owner->pi_blocked_on)
            chain_walk = 1;
    }
    else if (rt_mutex_cond_detect_deadlock(waiter, chwalk))
    {
        chain_walk = 1;
    }

    /* Store the lock on which owner is blocked or NULL */
    next_lock = task_blocked_on_lock(owner);

    raw_spin_unlock(&owner->pi_lock);
    /*
     * Even if full deadlock detection is on, if the owner is not
     * blocked itself, we can avoid finding this out in the chain
     * walk.
     */
    if (!chain_walk || !next_lock)
        return 0;

    /*
     * The owner can't disappear while holding a lock,
     * so the owner struct is protected by wait_lock.
     * Gets dropped in rt_mutex_adjust_prio_chain()!
     */
    get_task_struct(owner);

    raw_spin_unlock_irq_wake(&lock->wait_lock, wake_q);

    res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
                                     next_lock, waiter, task);

    raw_spin_lock_irq(&lock->wait_lock);

    return res;
}

/*
 * Remove the top waiter from the current tasks pi waiter tree and
 * queue it up.
 *
 * Called with lock->wait_lock held and interrupts disabled.
 */
static void __sched mark_wakeup_next_waiter(struct rt_wake_q_head *wqh,
                                            struct rt_mutex_base *lock)
{
    struct rt_mutex_waiter *waiter;

    lockdep_assert_held(&lock->wait_lock);

    raw_spin_lock(&current->pi_lock);

    waiter = rt_mutex_top_waiter(lock);

    /*
     * Remove it from current->pi_waiters and deboost.
     *
     * We must in fact deboost here in order to ensure we call
     * rt_mutex_setprio() to update p->pi_top_task before the
     * task unblocks.
     */
    rt_mutex_dequeue_pi(current, waiter);
    rt_mutex_adjust_prio(lock, current);

    /*
     * As we are waking up the top waiter, and the waiter stays
     * queued on the lock until it gets the lock, this lock
     * obviously has waiters. Just set the bit here and this has
     * the added benefit of forcing all new tasks into the
     * slow path making sure no task of lower priority than
     * the top waiter can steal this lock.
     */
    lock->owner = (void *)RT_MUTEX_HAS_WAITERS;

    /*
     * We deboosted before waking the top waiter task such that we don't
     * run two tasks with the 'same' priority (and ensure the
     * p->pi_top_task pointer points to a blocked task). This however can
     * lead to priority inversion if we would get preempted after the
     * deboost but before waking our donor task, hence the preempt_disable()
     * before unlock.
     *
     * Pairs with preempt_enable() in rt_mutex_wake_up_q();
     */
    preempt_disable();
    rt_mutex_wake_q_add(wqh, waiter);
    raw_spin_unlock(&current->pi_lock);
}

static int __sched __rt_mutex_slowtrylock(struct rt_mutex_base *lock)
{
    int ret = try_to_take_rt_mutex(lock, current, NULL);

    /*
     * try_to_take_rt_mutex() sets the lock waiters bit
     * unconditionally. Clean this up.
     */
    fixup_rt_mutex_waiters(lock, true);

    return ret;
}

/*
 * Slow path try-lock function:
 */
static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock)
{
    unsigned long flags;
    int ret;

    /*
     * If the lock already has an owner we fail to get the lock.
     * This can be done without taking the @lock->wait_lock as
     * it is only being read, and this is a trylock anyway.
     */
    if (rt_mutex_owner(lock))
        return 0;

    /*
     * The mutex has currently no owner. Lock the wait lock and try to
     * acquire the lock. We use irqsave here to support early boot calls.
     */
    raw_spin_lock_irqsave(&lock->wait_lock, flags);

    ret = __rt_mutex_slowtrylock(lock);

    raw_spin_unlock_irqrestore(&lock->wait_lock, flags);

    return ret;
}

static __always_inline int __rt_mutex_trylock(struct rt_mutex_base *lock)
{
    if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
        return 1;

    return rt_mutex_slowtrylock(lock);
}

/*
 * Slow path to release a rt-mutex.
 */
static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock)
{
    DEFINE_RT_WAKE_Q(wqh);
    unsigned long flags;

    /* irqsave required to support early boot calls */
    raw_spin_lock_irqsave(&lock->wait_lock, flags);

    debug_rt_mutex_unlock(lock);

    /*
     * We must be careful here if the fast path is enabled. If we
     * have no waiters queued we cannot set owner to NULL here
     * because of:
     *
     * foo->lock->owner = NULL;
     *			rtmutex_lock(foo->lock);   <- fast path
     *			free = atomic_dec_and_test(foo->refcnt);
     *			rtmutex_unlock(foo->lock); <- fast path
     *			if (free)
     *				kfree(foo);
     * raw_spin_unlock(foo->lock->wait_lock);
     *
     * So for the fastpath enabled kernel:
     *
     * Nothing can set the waiters bit as long as we hold
     * lock->wait_lock. So we do the following sequence:
     *
     *	owner = rt_mutex_owner(lock);
     *	clear_rt_mutex_waiters(lock);
     *	raw_spin_unlock(&lock->wait_lock);
     *	if (cmpxchg(&lock->owner, owner, 0) == owner)
     *		return;
     *	goto retry;
     *
     * The fastpath disabled variant is simple as all access to
     * lock->owner is serialized by lock->wait_lock:
     *
     *	lock->owner = NULL;
     *	raw_spin_unlock(&lock->wait_lock);
     */
    while (!rt_mutex_has_waiters(lock))
    {
        /* Drops lock->wait_lock ! */
        if (unlock_rt_mutex_safe(lock, flags) == true)
            return;
        /* Relock the rtmutex and try again */
        raw_spin_lock_irqsave(&lock->wait_lock, flags);
    }

    /*
     * The wakeup next waiter path does not suffer from the above
     * race. See the comments there.
     *
     * Queue the next waiter for wakeup once we release the wait_lock.
     */
    mark_wakeup_next_waiter(&wqh, lock);
    raw_spin_unlock_irqrestore(&lock->wait_lock, flags);

    rt_mutex_wake_up_q(&wqh);
}

static __always_inline void __rt_mutex_unlock(struct rt_mutex_base *lock)
{
    if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
        return;

    rt_mutex_slowunlock(lock);
}

#ifdef CONFIG_SMP
static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
                                  struct rt_mutex_waiter *waiter,
                                  struct task_struct *owner)
{
    bool res = true;

    rcu_read_lock();
    for (;;)
    {
        /* If owner changed, trylock again. */
        if (owner != rt_mutex_owner(lock))
            break;
        /*
         * Ensure that @owner is dereferenced after checking that
         * the lock owner still matches @owner. If that fails,
         * @owner might point to freed memory. If it still matches,
         * the rcu_read_lock() ensures the memory stays valid.
         */
        barrier();
        /*
         * Stop spinning when:
         *  - the lock owner has been scheduled out
         *  - current is not longer the top waiter
         *  - current is requested to reschedule (redundant
         *    for CONFIG_PREEMPT_RCU=y)
         *  - the VCPU on which owner runs is preempted
         */
        if (!owner_on_cpu(owner) || need_resched() ||
            !rt_mutex_waiter_is_top_waiter(lock, waiter))
        {
            res = false;
            break;
        }
        cpu_relax();
    }
    rcu_read_unlock();
    return res;
}
#else
static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
                                  struct rt_mutex_waiter *waiter,
                                  struct task_struct *owner)
{
    return false;
}
#endif

/*
 * Functions required for:
 *	- rtmutex, futex on all kernels
 *	- mutex and rwsem substitutions on RT kernels
 */

/*
 * Remove a waiter from a lock and give up
 *
 * Must be called with lock->wait_lock held and interrupts disabled. It must
 * have just failed to try_to_take_rt_mutex().
 */
static void __sched remove_waiter(struct rt_mutex_base *lock,
                                  struct rt_mutex_waiter *waiter)
{
    bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
    struct task_struct *owner = rt_mutex_owner(lock);
    struct rt_mutex_base *next_lock;

    lockdep_assert_held(&lock->wait_lock);

    raw_spin_lock(&current->pi_lock);
    rt_mutex_dequeue(lock, waiter);
    current->pi_blocked_on = NULL;
    raw_spin_unlock(&current->pi_lock);

    /*
     * Only update priority if the waiter was the highest priority
     * waiter of the lock and there is an owner to update.
     */
    if (!owner || !is_top_waiter)
        return;

    raw_spin_lock(&owner->pi_lock);

    rt_mutex_dequeue_pi(owner, waiter);

    if (rt_mutex_has_waiters(lock))
        rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));

    rt_mutex_adjust_prio(lock, owner);

    /* Store the lock on which owner is blocked or NULL */
    next_lock = task_blocked_on_lock(owner);

    raw_spin_unlock(&owner->pi_lock);

    /*
     * Don't walk the chain, if the owner task is not blocked
     * itself.
     */
    if (!next_lock)
        return;

    /* gets dropped in rt_mutex_adjust_prio_chain()! */
    get_task_struct(owner);

    raw_spin_unlock_irq(&lock->wait_lock);

    rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
                               next_lock, NULL, current);

    raw_spin_lock_irq(&lock->wait_lock);
}

/**
 * rt_mutex_slowlock_block() - Perform the wait-wake-try-to-take loop
 * @lock:		 the rt_mutex to take
 * @ww_ctx:		 WW mutex context pointer
 * @state:		 the state the task should block in (TASK_INTERRUPTIBLE
 *			 or TASK_UNINTERRUPTIBLE)
 * @timeout:		 the pre-initialized and started timer, or NULL for none
 * @waiter:		 the pre-initialized rt_mutex_waiter
 * @wake_q:		 wake_q of tasks to wake when we drop the lock->wait_lock
 *
 * Must be called with lock->wait_lock held and interrupts disabled
 */
static int __sched rt_mutex_slowlock_block(struct rt_mutex_base *lock,
                                           struct ww_acquire_ctx *ww_ctx,
                                           unsigned int state,
                                           struct hrtimer_sleeper *timeout,
                                           struct rt_mutex_waiter *waiter,
                                           struct wake_q_head *wake_q)
    __releases(&lock->wait_lock) __acquires(&lock->wait_lock)
{
    struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
    struct task_struct *owner;
    int ret = 0;

    for (;;)
    {
        /* Try to acquire the lock: */
        if (try_to_take_rt_mutex(lock, current, waiter))
            break;

        if (timeout && !timeout->task)
        {
            ret = -ETIMEDOUT;
            break;
        }
        if (signal_pending_state(state, current))
        {
            ret = -EINTR;
            break;
        }

        if (build_ww_mutex() && ww_ctx)
        {
            ret = __ww_mutex_check_kill(rtm, waiter, ww_ctx);
            if (ret)
                break;
        }

        if (waiter == rt_mutex_top_waiter(lock))
            owner = rt_mutex_owner(lock);
        else
            owner = NULL;
        raw_spin_unlock_irq_wake(&lock->wait_lock, wake_q);

        if (!owner || !rtmutex_spin_on_owner(lock, waiter, owner))
            rt_mutex_schedule();

        raw_spin_lock_irq(&lock->wait_lock);
        set_current_state(state);
    }

    __set_current_state(TASK_RUNNING);
    return ret;
}

static void __sched rt_mutex_handle_deadlock(int res, int detect_deadlock,
                                             struct rt_mutex_base *lock,
                                             struct rt_mutex_waiter *w)
{
    /*
     * If the result is not -EDEADLOCK or the caller requested
     * deadlock detection, nothing to do here.
     */
    if (res != -EDEADLOCK || detect_deadlock)
        return;

    if (build_ww_mutex() && w->ww_ctx)
        return;

    raw_spin_unlock_irq(&lock->wait_lock);

    WARN(1, "rtmutex deadlock detected\n");

    while (1)
    {
        set_current_state(TASK_INTERRUPTIBLE);
        rt_mutex_schedule();
    }
}

/**
 * __rt_mutex_slowlock - Locking slowpath invoked with lock::wait_lock held
 * @lock:	The rtmutex to block lock
 * @ww_ctx:	WW mutex context pointer
 * @state:	The task state for sleeping
 * @chwalk:	Indicator whether full or partial chainwalk is requested
 * @waiter:	Initializer waiter for blocking
 * @wake_q:	The wake_q to wake tasks after we release the wait_lock
 */
static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
                                       struct ww_acquire_ctx *ww_ctx,
                                       unsigned int state,
                                       enum rtmutex_chainwalk chwalk,
                                       struct rt_mutex_waiter *waiter,
                                       struct wake_q_head *wake_q)
{
    struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
    struct ww_mutex *ww = ww_container_of(rtm);
    int ret;

    lockdep_assert_held(&lock->wait_lock);

    /* Try to acquire the lock again: */
    if (try_to_take_rt_mutex(lock, current, NULL))
    {
        if (build_ww_mutex() && ww_ctx)
        {
            __ww_mutex_check_waiters(rtm, ww_ctx, wake_q);
            ww_mutex_lock_acquired(ww, ww_ctx);
        }
        return 0;
    }

    set_current_state(state);

    trace_contention_begin(lock, LCB_F_RT);

    ret = task_blocks_on_rt_mutex(lock, waiter, current, ww_ctx, chwalk, wake_q);
    if (likely(!ret))
        ret = rt_mutex_slowlock_block(lock, ww_ctx, state, NULL, waiter, wake_q);

    if (likely(!ret))
    {
        /* acquired the lock */
        if (build_ww_mutex() && ww_ctx)
        {
            if (!ww_ctx->is_wait_die)
                __ww_mutex_check_waiters(rtm, ww_ctx, wake_q);
            ww_mutex_lock_acquired(ww, ww_ctx);
        }
    }
    else
    {
        __set_current_state(TASK_RUNNING);
        remove_waiter(lock, waiter);
        rt_mutex_handle_deadlock(ret, chwalk, lock, waiter);
    }

    /*
     * try_to_take_rt_mutex() sets the waiter bit
     * unconditionally. We might have to fix that up.
     */
    fixup_rt_mutex_waiters(lock, true);

    trace_contention_end(lock, ret);

    return ret;
}

static inline int __rt_mutex_slowlock_locked(struct rt_mutex_base *lock,
                                             struct ww_acquire_ctx *ww_ctx,
                                             unsigned int state,
                                             struct wake_q_head *wake_q)
{
    struct rt_mutex_waiter waiter;
    int ret;

    rt_mutex_init_waiter(&waiter);
    waiter.ww_ctx = ww_ctx;

    ret = __rt_mutex_slowlock(lock, ww_ctx, state, RT_MUTEX_MIN_CHAINWALK,
                              &waiter, wake_q);

    debug_rt_mutex_free_waiter(&waiter);
    return ret;
}

/*
 * rt_mutex_slowlock - Locking slowpath invoked when fast path fails
 * @lock:	The rtmutex to block lock
 * @ww_ctx:	WW mutex context pointer
 * @state:	The task state for sleeping
 */
static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
                                     struct ww_acquire_ctx *ww_ctx,
                                     unsigned int state)
{
    DEFINE_WAKE_Q(wake_q);
    unsigned long flags;
    int ret;

    /*
     * Do all pre-schedule work here, before we queue a waiter and invoke
     * PI -- any such work that trips on rtlock (PREEMPT_RT spinlock) would
     * otherwise recurse back into task_blocks_on_rt_mutex() through
     * rtlock_slowlock() and will then enqueue a second waiter for this
     * same task and things get really confusing real fast.
     */
    rt_mutex_pre_schedule();

    /*
     * Technically we could use raw_spin_[un]lock_irq() here, but this can
     * be called in early boot if the cmpxchg() fast path is disabled
     * (debug, no architecture support). In this case we will acquire the
     * rtmutex with lock->wait_lock held. But we cannot unconditionally
     * enable interrupts in that early boot case. So we need to use the
     * irqsave/restore variants.
     */
    raw_spin_lock_irqsave(&lock->wait_lock, flags);
    ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state, &wake_q);
    raw_spin_unlock_irqrestore_wake(&lock->wait_lock, flags, &wake_q);
    rt_mutex_post_schedule();

    return ret;
}

static __always_inline int __rt_mutex_lock(struct rt_mutex_base *lock,
                                           unsigned int state)
{
    lockdep_assert(!current->pi_blocked_on);

    if (likely(rt_mutex_try_acquire(lock)))
        return 0;

    return rt_mutex_slowlock(lock, NULL, state);
}

#ifdef RT_MUTEX_BUILD_SPINLOCKS
/*
 * Functions required for spin/rw_lock substitution on RT kernels
 */

/**
 * rtlock_slowlock_locked - Slow path lock acquisition for RT locks
 * @lock:	The underlying RT mutex
 * @wake_q:	The wake_q to wake tasks after we release the wait_lock
 */
static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock,
                                           struct wake_q_head *wake_q)
    __releases(&lock->wait_lock) __acquires(&lock->wait_lock)
{
    struct rt_mutex_waiter waiter;
    struct task_struct *owner;

    lockdep_assert_held(&lock->wait_lock);

    if (try_to_take_rt_mutex(lock, current, NULL))
        return;

    rt_mutex_init_rtlock_waiter(&waiter);

    /* Save current state and set state to TASK_RTLOCK_WAIT */
    current_save_and_set_rtlock_wait_state();

    trace_contention_begin(lock, LCB_F_RT);

    task_blocks_on_rt_mutex(lock, &waiter, current, NULL, RT_MUTEX_MIN_CHAINWALK, wake_q);

    for (;;)
    {
        /* Try to acquire the lock again */
        if (try_to_take_rt_mutex(lock, current, &waiter))
            break;

        if (&waiter == rt_mutex_top_waiter(lock))
            owner = rt_mutex_owner(lock);
        else
            owner = NULL;
        raw_spin_unlock_irq_wake(&lock->wait_lock, wake_q);

        if (!owner || !rtmutex_spin_on_owner(lock, &waiter, owner))
            schedule_rtlock();

        raw_spin_lock_irq(&lock->wait_lock);
        set_current_state(TASK_RTLOCK_WAIT);
    }

    /* Restore the task state */
    current_restore_rtlock_saved_state();

    /*
     * try_to_take_rt_mutex() sets the waiter bit unconditionally.
     * We might have to fix that up:
     */
    fixup_rt_mutex_waiters(lock, true);
    debug_rt_mutex_free_waiter(&waiter);

    trace_contention_end(lock, 0);
}

static __always_inline void __sched rtlock_slowlock(struct rt_mutex_base *lock)
{
    unsigned long flags;
    DEFINE_WAKE_Q(wake_q);

    raw_spin_lock_irqsave(&lock->wait_lock, flags);
    rtlock_slowlock_locked(lock, &wake_q);
    raw_spin_unlock_irqrestore_wake(&lock->wait_lock, flags, &wake_q);
}

#endif /* RT_MUTEX_BUILD_SPINLOCKS */
